random missfire

[Bushman]

after parking up my lil S for a week or so at work whilst I was away on business, I came back to a random misfire mainly on 4 and 6 according to my OBD reader. starts beautifully every time, runs perfectly for a couple of miles then drops either 1 or 2 cyls whilst at low revs. the CEL flashes a few times. if I am quick enough, reving it up over 3000 rpm brings 6 cyls back in most times but as soon as the revs drop, back on 4. switch the car off then restart it, straight back on 6, back to normal for a while. resetting the fault with the ign eliminates shitty fuel so I thought cracked plug top coils. just got my tame mechy with a 4 poster to change my plugs and fit British made uprated Benchmark coils and whilst he was at it, a cam position sensor.

This was flagged on several forums from all around the world as it appears that this exact fault is quite common but nobody seems to conclusively pin it down to a particular fault, but cam position sensors were a likely candidate.  On the way home, same fault. The service centre next to my tame mechy had all the latest Porsche diagnostic software on his machine, loves Porkers but didn't just want to restrict himself to one brand so does all German makes. anyway, he diagnosed camshaft position solenoids as the problem. Some research suggests that before replacing them as they are about £250 each, to remove them and give them  good solvent clean as the mesh filter gauze inside gets blocked with oil sludges and deposits and the solenoids stick.

Question, has anybody else come across this issue and did cleaning out the solenoids cure the problem. cheers guys.

[GlosRich]

Have you tested your battery is that ok? Is the alternator charging properly?

[jcm987]

@Bushman I had a similar problem about a year ago after leaving the car for months without driving. Car started misfiring, most noticeable at low revs. The solution was a replacement solenoid and thorough cleaning. Fortunately I already had the car booked into a Porsche Indy for something else and they fixed it in a day. If I remember correctly, parts were £250 plus labour etc... 

[Bushman]

thanks guys.

Rich, battery is fairly new and is a high ampage Bosch. alternator is fine.

[pstarkey]

Had a similar issue turned out to be the VVT solenoid - got various OBD error codes relating to misfire and 'value lift control' 1361, 1363, 137, 1359 replaced both solenoids circa £100 each did both banks, easy to get to once wheel off and dirt shield removed.  

[DKR_77]

Replaced mine on my 987, same issues as you're describing.  I never tried cleaning though.